This invention relates to the automatic control of vehicle headlamp intensity in response to the sensed light in front of the vehicle. Such sensed light is generally due to the headlamps of oncoming vehicles, although it may also be from the taillamps of vehicles being followed.
Such systems generally include feedback for hysteresis in switching back and forth from low to high beams in response to sensed light, in order to produce sure switching in the normal manner. This hysteresis is immediate upon switching and produces a step change in the sensitivity of the system in the direction to require a significant reversal of light level to cause a switch back to the original state. The control of this invention modifies this hysteresis by allowing the sensitivity to return from the stepped value over time after switching. The control as claimed offers several benefits in system operation, including automatic correction of photocell memory and adjustment of system sensitivity to variations in sensor or headlamp aiming. In its operation, it tends to reduce the need for driver intervention via the driver sensitivity control, which leads to improved driver satisfaction with the system.